Tension roller for belt drives

ABSTRACT

The invention concerns a tension roller made of a plastic material for adjusting a tension in a belt drive, comprising a wheel (7) having an inner ring (9) and an outer ring (10) connected to each other by axially oriented, circumferentially spaced ribs (12) and by a central web (8), the wheel (7) being rotatably mounted on a support element (2) which bears by a running face against the belt (3). According to the invention, successive ribs (12) enclose different angles with reference to a central point of the wheel.

The invention concerns a tension roller, particularly for belt drives ofthe type made of a plastic material, a castable material or a materialspray-coated with a plastic material for adjusting a tension in a beltdrive, comprising a wheel having an inner ring and an outer ringconnected to each other by axially oriented, circumferentially spacedribs and by a central web, the wheel being rotatably mounted on asupport element which bears by a running face against a belt.

STATE OF THE ART

It is possible to adjust a desired belt tension in a belt drive with thehelp of a tension roller. From DE 32 26 419 A1, a tension roller isknown in which a wheel made of a plastic material is mounted on asupport element by means of a rolling bearing. The wheel includes aninner ring which is arranged rotationally fast on an outer ring of therolling bearing and is connected by a central web and by axiallyextending, circumferentially uniformly spaced ribs to an outer ring. Aconnection with the belt drive is established via a running face of theouter ring.

At certain speeds of rotation, the uniform spacing of the ribs can leadto a resonance accompanied by detrimental noise stimulation which isparticularly undesired in modern vehicles and detracts from comfort.

OBJECT OF THE INVENTION

It is an object of the invention to create a tension roller with reducedrunning noises.

THE INVENTION

The tension roller of the invention made of a plastic material, acastable material or a material spray-coated with a plastic material foradjusting a tension in a belt drive, comprising a wheel having an innerring and an outer ring connected to each other by axially oriented,circumferentially spaced ribs and by a central web, the wheel beingrotatably mounted on a support element which bears by a running faceagainst a belt, is characterized in that successive ribs (12, 32, 52)enclose different angles therebetween with reference to a central pointof the wheel (7, 27, 47).

The invention provides that the successive ribs of the wheel enclosedifferent angles therebetween with reference to a central point of thewheel. Compared to the hitherto generally used uniform rib spacing, thenon-uniform spacing of the ribs effectively eliminates resonanceformation and contributes in particular to meeting the requirement ofnoise optimization in belt drives of automobile engines.

Conditional upon their manufacturing process, the plastic wheels oftension rollers have certain circularity errors, i.e. the portions ofthe running face between the ribs comprise almost straight sectionsinstead of the desired curvature, so that the belt is periodicallytightened in the region of the ribs and slackened in the intermediateportions. This causes a stimulation of vibration of the belt guided onthe running face of the plastic wheel, and at certain speeds ofrotation, the vibrations are intensified in the case of uniformly spacedribs into a resonance accompanied by noise stimulation.

Due to the non-uniform spacing of the ribs as provided by the invention,different distances are advantageously obtained on the running face sothat no uniform excitation of the belt is possible and the running noiseof the tension roller is not detrimentally increased. The advantageousminimum distance between two adjacent ribs is 0.5 degrees or more.

In one embodiment of the invention, the ribs are arranged withperiodically recurring angular dimensions. It is possible, for example,to choose a rib arrangement in which a particular angular distanceoccurs after every five ribs. If this measure is implemented, abalancing of the tension roller required for high speeds of rotation canadvantageously be dispensed with or at least simplified.

To avoid excessively large differences in rib spacing, recites a maximumdifference of <5 mm for all distances between ribs in the region of therunning face is provided.

Another embodiment provides for the arrangement of intermediate ribs inalternation with standard ribs. Intermediate ribs are advantageouslysuited for tension rollers with large diameters because they enablelarge distances to be obtained at the ends of the ribs in the region ofthe running face despite a tight arrangement at the feet of the ribs.Thus the distances at the rib ends can be advantageously influenced bythe use of intermediate ribs. The intermediate ribs permit the formationof an approximately fully circular running face with the distancesbetween all ribs being different from one another.

The intermediate ribs may end in an intermediate ring which increasesthe strength of the wheel and is also connected to all other ribs.

A further measure contributing to a reduction of the running noise ofthe tension roller is to dispose covering disks laterally on the wheel.This also excludes a possibly disadvantageous open arrangement of theribs which increases the running noise. To obtain a noise-optimizedtension roller, it is advantageous to use the covering disks in additionto the non-uniform spacing of the ribs.

Further features of the invention will become evident from the drawingsand their description:

FIG. 1 is a front view of a preferred embodiment of the tension rollerof the invention;

FIG. 2 is a longitudinal section taken along line A--A of the tensionroller of FIG. 1;

FIG. 3 is a front view of a tension roller of the invention comprisingintermediate ribs;

FIG. 4 is a longitudinal section through a tension roller comprisinglateral covering disks.

The structure of a tension roller 1 according to the invention will atfirst be described with reference to FIGS. 1 and 2. The tension roller 1comprises a support element 2 which is connected, for example, to atensioner which serves to pre-tension a belt 3 of a belt drive. On theouter peripheral surface 4 of the pot-shaped support element 2 is guideda rolling bearing 5 on whose outer ring 6, a wheel 7 is positionallyfixed. As an alternative to the rolling bearing shown here, it is alsopossible to use a series ball bearing with an inner ring guided on thesupport element 2 and an outer ring spray-coated, for example, with thematerial of the wheel 7. The wheel 7 made of a plastic material, orspray-coated with a plastic material, possesses an H-shapedcross-section with a central web 8 connecting an inner ring 9 and anouter ring 10 to each other. This configuration leads to the formationof U-shaped empty spaces 11 in which axially extending ribs 12 arearranged to provide stiffness. The belt 3 is guided on a running face 13of the outer ring 10. As can be seen in FIG. 1, the ribs 12 aredifferently spaced from one another, see distances referenced at "a" and"b".

FIG. 3 shows a tension roller 21 whose support element 22 has smallerdimensions. The ribs 32 which extend from the inner ring 29 to the outerring 30 therefore have a larger radial length. To obtain an adequatesupport of the running face 33 by the ribs, there are providedintermediate ribs 36 extending from the outer ring 30 to theintermediate ring 35. This configuration leads to the formation ofdiffering empty spaces. The outer empty space 31 extends between theouter ring 30 and the intermediate ring 35 and is defined laterally by arib 32 and an intermediate rib 36. The inner empty space 34 is formed inthe region between the inner ring 29 and the intermediate ring 35 and isfurther delimited on each side by a rib 32.

In another embodiment of the tension roller of the invention shown inFIG. 4, parts identical with the first example of embodiment shown inFIG. 2 are designated by the same reference numerals so that referencecan be made to the first example of embodiment for their description.

The tension roller 41 of FIG. 4 comprises additional means to helpprevent detrimental noise stimulation by the ribs. This is obtained byclosing the empty spaces 51 laterally with covering disks 53, 54, eachof which connects the inner ring 49 to the outer ring 50 on the outsidewhile bearing laterally against the ribs 52. The covering disks 53, 54are fixed by rims 55, 56 arranged on the inner and the outer rings 49,50 for locking with the covering disks 53, 54.

The wheel 47 thus has a closed, circular ring-shaped boxlikeconfiguration which contributes to an effective reduction of noise.

    ______________________________________                                        List of Reference Numerals                                                    ______________________________________                                                   1  Tension roller                                                             2  Support element                                                            3  Belt                                                                       4  Peripheral surface                                                         5  Rolling bearing                                                            6  Outer ring                                                                 7  Wheel                                                                      8  Central web                                                                9  Inner ring                                                                10  Outer ring                                                                11  Empty space                                                               12  Rib                                                                       13  Running face                                                              21  Tension roller                                                            22  Support element                                                           27  Wheel                                                                     29  Inner ring                                                                30  Outer ring                                                                31  Empty space (outer)                                                       32  Rib                                                                       33  Running face                                                              34  Empty space (inner)                                                       35  Intermediate ring                                                         36  Intermediate rib                                                          41  Tension roller                                                            47  Wheel                                                                     49  Inner ring                                                                50  Outer ring                                                                51  Empty space                                                               52  Rib                                                                       53  Covering disk                                                             54  Covering disk                                                             55  Rim                                                                       56  Rim                                                             ______________________________________                                    

We claim:
 1. A tension roller made of a plastic material, a castablematerial or a material spray-coated with a plastic material foradjusting a tension in a belt drive, comprising a wheel having an innerring and an outer ring connected to each other by axially oriented,circumferentially spaced ribs and by a central web, the wheel beingrotatably mounted on a support element which bears by a running faceagainst a belt, characterized in that successive ribs (12, 32, 52)enclose different angles therebetween with reference to a central pointof the wheel (7, 27, 47).
 2. A tension roller of claim 1 wherein anarrangement of the ribs (12, 32, 52) comprises periodically recurringangular dimensions.
 3. A tension roller of claim 1 wherein a differenceof a distance dimension between the ribs (12, 32, 52) is less than 5 mm.4. A tension roller of claim 1 wherein the ribs (32) are arranged inalternation with intermediate ribs (36).
 5. A tension roller of claim 4wherein the intermediate ribs (36) end in an intermediate ring (35). 6.A tension roller of claim 1 wherein on both sides of the wheel (47) arearranged covering disks (53, 54) which bear axially against the ribs(52) and connect the inner ring (49) to the outer ring (50).